1. Field of the Invention
The present invention relates to an integrated nozzle plate and a method for the forming of the integrated nozzle plate. More particularly, the present invention relates to an integrated nozzle plate formed of multiple resist layers placed directly on a heater chip in a batch manufacturing process using a photolithographic method.
2. Description of the Related Art
Presently, print heads for inkjet printers are manufactured in a process employing several independent steps. This normally entails forming a nozzle plate formed using an excimer laser to ablate nozzles, firing chambers and ink channels in the nozzle plate. The excimer lasers used to create the nozzle plates are extremely large and expensive devices. Once the nozzle plate is formed using the excimer laser, the nozzle plate is aligned and bonded to a heater chip. The heater chip is composed of heating elements that quickly heat ink in individual firing (vaporization) chambers to the point of vaporization. This results in the ejecting of ink through nozzle holes located in the nozzle plate. As heater chips become smaller, more nozzles (typically of smaller dimension) are required to achieve better printing performance and the alignment step between the heater chip and the nozzle plate becomes even more critical.
Current nozzle plate to heater chip alignment requirements specify a tolerance of less than plus or minus 15 microns. Equipment has been developed that mates laser ablated nozzle nozzles plates with heater chips within the tolerances required. This equipment can operate at high speeds and is generally very consistent and accurate. However, the cost of such equipment is extremely high. Further, even though extremely accurate and consistent, the equipment is not perfect and some misalignment does occur. Misalignment of the nozzle plate creates a print head that either has extremely poor print quality or fails to function entirely and these print heads must be rejected. Therefore, the cost of manufacturing a high quality print head using a separate laser ablated nozzle plate and heater chip is very high. This is due to the high cost of the equipment used to ablate the nozzle plates and mate them within the extremely high tolerances to the heater chips. Further, the cost of rejects also adds to the cost of manufacturing.
In addition to the foregoing method of manufacturing a print head, the following methods of manufacturing inkjet print heads are disclosed in the prior art discussed below.
U.S. Pat. No. 5,686,224 to O'Neill discloses the creation of ink channel structures in photoresist material for a side shooter print head. A separate glass plate is then used to close off the open tops of these structures. This patent also describes the use of a variable grade (gray scale mask) to limit the amount of UV light transmitted to certain areas of a photoresist material. To create this structure, O'Neill requires multiple layers of resist to be spun one on top of the other. This process is difficult to use in a manufacturing environment and crisp defined structures are not possible using a variable grade mask. Instead the structures created by O'Neill using UV light exposure through a variable grade mask would tend to be somewhat ragged. In a printing system that demands accuracy in the features used to eject ink jet droplets, this approach would not generate the desired accuracy.
U.S. Pat. No. 5,697,144 to Mitani et al. discloses a method for producing a print head for a printer using thin film processes only. A 1,600 dpi (dot per inch) print head with nozzles arranged two dimensionally on a substrate is possible using this method. Ink channels and nozzle holes are formed using silicon anisotropic etching from both sides of the silicon wafer substrate. After connecting the nozzle plate to the silicon wafer substrate, nozzles are formed in the nozzle plate using photo-etching techniques.
European Patent Application EP 0 749-835 A2 to Inada et al. discloses a method of manufacturing an inkjet print head using photolithographic techniques. The process involves first placing a positive resist layer on a substrate. Photolithographic techniques are then used to form the structures of nozzles, chambers and channels.
However, none of the foregoing prior art references is able to create a print head nozzle plate using photolithographic methods directly on a heater chip to produce complex and highly precise structures in a cost-effective manner.
Thus, a need exists for a method of forming nozzle plates directly on heater chips through a simple and low cost manufacturing method. Further, this manufacturing method must be able to produce a consistent product with very high tolerances.